This invention relates generally to apparatus and methods for generating coherent electromagnetic radiation, and, more particularly, relates to tunable free electron laser (FEL) apparatus and methods for generating coherent radiation over a wide range of wavelengths.
The importance of a versatile and convenient far infra-red (FIR) submillimeter (submm) source is a direct consequence of the large range of research opportunities and technical applications associated with this spectral region. Examples of opportunities may be gathered under the broad headings of spectroscopy and technology development.
Spectroscopy applications include surface science, condensed-matter phenomena, excitations in high T.sub.c superconductor, laser chemistry, radio astronomy, diagnostics in thermonuclear plasmas, conformational excitations in biomolecules, gas phase spectroscopy (rotational excitations).
Technology development activities include submm radar, Radar modeling, countermeasures for FIR systems, space communications, compact high-gradient accelerator research, plasma heating, isotope separation.
In view of the importance of the FIR spectral range, considerable effort has been expended in this area. During the preceding three decades, much of this work has centered on developing improved detectors and better spectroscopic systems. At present, these systems are nearing perfection. Fundamental limits to detector sensitivity are now approached with liquid-helium-cooled detectors. There have also been major advances in both spectrometer design and in the fabrication of signal processing components. Further development in the latter categories can be expected, but research emphasis is now switching to sources. Increased source power automatically provides greater signal-to-noise ratio and if stability is adequate, better resolution. Furthermore, the study and exploitation of nonlinear and transient processes which are not possible with continuum and other low-power sources, now become accessible options.
During the last decade-and-a-half there have been new additions to the FIR submm source population and continued development of older concepts. These include microwave tubes, impatt diodes, gyrotrons, FIR lasers, semiconductor lasers, and FELS.